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Glossary · Energy industry & energy transition

Bidding zone

bidding zone electricity market grid congestion electricity price market design

A bidding zone is a geographically delimited area of wholesale electricity trading. Within this area, bids are treated as if electrical energy could be traded without grid-related restrictions. EU law describes the bidding zone, in essence, as the largest geographical area within which market participants can exchange energy without capacity allocation being required. In the coupled European day-ahead market, a single wholesale price therefore applies to all successful bids in a zone for each market time unit. The bidding zone is neither a technical installation nor a physical measured quantity. It is a market boundary: it determines the area in which the price is formed uniformly and at which borders transmission capacity explicitly enters price formation.

The bidding zone itself has no unit. What can be measured is the price formed within it. It is usually stated in euros per megawatt hour. Energy quantities are traded in megawatt hours, while transmission capacity between bidding zones is stated in megawatts. Since the delivery day of 1 October 2025, the price in the European single day-ahead coupling (SDAC) has been determined for quarter-hours in all bidding zones, no longer for hours. Since then, an hourly price has at most been published as an average of four quarter-hour prices. The bidding zone thus links market variables such as price, bid and traded volume with a technical limit of the power system: electricity cannot be transported through a grid without limits, even if the market calculates this way within the zone.

Distinction from price zone, control area and grid area

In everyday usage, bidding zone is often equated with price zone. This is usually unproblematic, because a common market price is formed in a bidding zone. Strictly speaking, "bidding zone" refers to the legally defined delineation of the market, whereas "price zone" refers to the effect on price formation. Coupled neighbouring zones can even temporarily have the same price if there is no congestion between them. A bidding zone does not have to coincide with a country. Germany and Luxembourg form a common bidding zone. Italy, Sweden, Norway and Denmark, by contrast, are divided into several bidding zones.

A bidding zone is also not a control area. Control areas belong to operational grid management. They determine which transmission system operator is responsible for load-frequency control, system balancing and the settlement of balancing energy. Germany has four control areas, operated by 50Hertz, Amprion, TenneT and TransnetBW. Together with Luxembourg, however, it forms only one bidding zone. Grid areas, in turn, describe the ownership, operation and connection responsibilities of grid operators in the transmission or distribution grid. Many grid areas can lie within one bidding zone without each of them having its own wholesale prices.

Nor can the bidding zone be equated with the end-customer price. Households and businesses do not simply pay the exchange price of their zone. Their electricity price additionally includes network charges, levies, taxes and supply costs. The supplier's procurement strategy and contract risks also have an effect. The zonal exchange price is an important part of procurement costs, but on its own explains neither the electricity bill nor the regional distribution of grid costs.

How a bidding zone works in the electricity market

In the European electricity market, generators, traders, storage operators, suppliers and larger consumers submit buy and sell bids. Within a bidding zone, these bids are brought together. Individual lines within the zone do not enter the price calculation as a constraint. Between zones, by contrast, the common coupling algorithm takes the available transmission capacity into account and allocates it where it brings the greatest welfare gain. Put simply, electricity flows from cheaper to more expensive zones until prices converge or capacity is exhausted. In Central Europe, the flow-based method is predominantly used for this. It looks not only at individual border lines but models how trades affect critical network elements, including those within a zone. Part of this capacity must be made available for cross-zonal trade.

A clear incentive follows from this: within a large bidding zone, what counts for the wholesale price is not the exact location of a plant but only its bid. A wind farm in Schleswig-Holstein, a gas-fired power plant in Bavaria and an industrial company in North Rhine-Westphalia see the same price in the day-ahead market. The market assumes that transport within the zone is possible. If the grid physically cannot handle this transport task, the transmission system operators must intervene after the market result.

These interventions are usually summarised under the term redispatch. Plants in front of a grid bottleneck are ramped down and plants behind it are ramped up, so that no line is overloaded and system security is maintained. Redispatch is not misconduct by individual market participants. It is the consequence of a zonal market design when the real grid is more constrained than the delineation of the bidding zone reflects in price formation.

Legal framework in the EU

The relevant instrument for the EU is Regulation (EU) 2019/943 on the internal market for electricity, supplemented by the CACM Guideline, Regulation (EU) 2015/1222. Under Article 14 of Regulation 2019/943, bidding zone borders are to be based on long-term, structural congestion in the transmission grid. The recitals require that bidding zones enable liquidity, efficient congestion management and effective locational signals. Cross-border capacity is not to be reduced in order to resolve congestion within a zone. Under Article 16, transmission system operators must make available at least 70 percent of the capacity of critical network elements for cross-zonal trade.

If a Member State identifies structural congestion, it has two options. It can redraw the bidding zone, or it can submit an action plan with measures such as grid reinforcement and grid optimisation. If it chooses the action plan, its bidding zone may not be changed against its will as long as it complies with the minimum capacity. As a last resort, the European Commission can decide on the delineation. A purely national procedure for splitting a zone is ruled out. Individual German federal states certainly cannot change the delineation.

Situation in Germany and Luxembourg

On 28 April 2025, ENTSO-E, the association of European transmission system operators, published its bidding zone review. The methodology had been specified by the regulatory agency ACER. For the German-Luxembourg zone, a split into five zones achieved the highest welfare gain in the calculation, with up to 339 million euros per year cited. At the same time, ENTSO-E stressed that this benefit must not be viewed in isolation. ACER considers the gains to be significantly underestimated. On 15 December 2025, the Federal Ministry for Economic Affairs published an "Action Plan Bidding Zone" and submitted it to the Commission. In it, Germany decides to retain the single zone and to reduce congestion mainly through grid expansion and congestion management. Since 1 January 2026, the 70 percent minimum value has applied without a transition path. If it is persistently missed, the EU procedure can be set in motion again. Politically, the topic is not settled. Northern German states and parts of the Bundestag continue to call for an open-ended review.

Why the size of the bidding zone is economically relevant

The size of a bidding zone determines which congestion becomes visible in the market price and which is dealt with only in grid operation. A large zone creates a single price across a wide area. This strengthens liquidity, simplifies trading, hedging and supply contracts, and avoids price jumps within the area. The drawback lies in the separation of market and grid. If generation and consumption are far apart and the transmission grid is insufficient, the single price can trigger transports that are physically not fully possible. The costs of the countermeasures then do not appear in the exchange price but are distributed via network charges or other levies.

Smaller zones translate structural congestion more strongly into prices. If there is a permanent bottleneck between two regions, the price on the generation side would tend to be lower and on the consumption side higher with separate zones, as long as transmission capacity is scarce. This changes the locational signals for new generation, storage, electrolysers and flexible industrial processes. A split, however, replaces neither grid expansion nor system operation nor reserves. It can also reduce the liquidity of forward markets and make hedging between zones more expensive. Whether a split is worthwhile depends on how persistent the congestion is, how high redispatch costs are, how stable the new zones would be and which transitional rules apply.

Typical misunderstandings

  • The bidding zone is not a pure representation of the grid. It is a market delineation with technical assumptions. The grid does not necessarily dictate a zone border, but at the same time every political decision has technical and economic consequences.

  • A single price does not mean that electricity can be transported without problems within the zone at all times. Physical load flows do not follow trade contracts but the electrical properties of the grid, that is, its impedances. Trade within a zone can therefore contribute to overloading at entirely different places, including in neighbouring countries as so-called loop flows or transit flows.

  • A split does not make electricity more expensive across the board but differentiates prices spatially. In surplus regions, wholesale prices could fall; in scarce consumption regions, they could rise. What reaches the end customer additionally depends on network charges, procurement, taxes, levies and political compensation rules.

  • The distribution question does not disappear in any market design. The costs of congestion are contained either in the wholesale price, in network charges, in state compensation mechanisms or in investment risks.

Connection with flexibility, grid expansion and security of supply

With the growing share of renewable energy, the bidding zone becomes more important, because generation is more weather-dependent and spatially concentrated. Wind power is often generated far from the large consumption centres. For flexibility, the zonal price is an important signal, but not always a sufficient one. If there is congestion within the zone, a storage unit or a flexible load can respond to the exchange price and thus act correctly in business terms, but from the grid's perspective in the wrong place. A strong transmission grid supports large bidding zones. Persistent congestion, by contrast, increases the tension between the single price and the actual grid loading. That is why grid expansion and zone delineation are closely linked.

For security of supply, the bidding zone replaces neither firm capacity nor grid operation management nor reserve instruments. It does, however, influence where scarcity prices arise and which investments pay off. If a consumption region permanently sees the same price as a distant generation region even though transport is regularly constrained, investment signals for dispatchable power plants, storage or flexible demand in the right place are weakened. Smaller zones send stronger regional signals but place higher demands on risk management and political acceptance. In short, the bidding zone marks the boundary at which the market translates grid scarcity into prices. Depending on the market design, the costs of congestion therefore appear in the price, in redispatch or in network charges.

Sources

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Edited by eCMS on 12.11.2026 05:05

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